Decoding apparatus and decoding method

ABSTRACT

Candidate limiting section  104  outputs to correlation value calculating section  105  only the TFCI coding sequences corresponding to TFCI numbers that are actually used based on TFCI numbers that are included in the group of TFCI numbers notified from a layer which is upper than the physical layer, correlation value calculating section  105  calculates the correlation values between the coding sequences outputted from candidate limiting section  104  and the received TFCI and stores the results in correlation value memory  106 , maximum value detecting section  107  notifies error correction decoding section  108  of the TFCI number corresponding to the maximum correlation value among the correlation values stored in correlation value memory  106 , and error correction decoding section  108  performs an error correction decoding on the data stored in data memory  103  according to the transmission format specified based on the notified TFCI number.

TECHNICAL FIELD

The present invention relates to a decoding apparatus and decodingmethod, specially relates to a decoding apparatus and decoding methodthat perform decoding of data based on transmission format informationtransmitted from a communication partner and on a determination resultof transmission format information.

BACKGROUND ART

In third generation mobile communication system using a CDMA technology,the execution of variable rate transmission by which the data rate ischanged for every TTI (Transmission Time Interval) unit is proposed. Thedetermination of data rate in the receiving side by a TFCI (TransportFormat Combination Indicator) which includes the transmission formatinformation is also proposed. Moreover, TTI is a data transmissionlength specified for every channel, and such a length is either 1, 2, 4or 8 frame(s).

Moreover, the transmission format of data (namely, block size of dataand the number of blocks of data) are specified by a TFCI number. Inother words, the data rate is specified by the TFCI number. According tothe specification of the third generation mobile communication systemspecified by 3GPP, the TFCI is shown by one number from among 1024numbers from the 0 through 1023, converted into a codeword correspondingto each number (hereinafter, a codeword corresponding to each number isreferred to as “TFCI coding sequence”) and then transmitted.

In the receiving side which receives the TFCI, the correlation valuesbetween each of the 1024 TFCI coding sequences which are specifiedbeforehand and the actually received TFCI are calculated by the decodingapparatus, and the number corresponding to the correlation value whichis maximum among the 1024 calculated correlation values is determined asthe received TFCI number. Then, decoding apparatus performs decoding ofdata based on transmission format specified by the determined TFCInumber.

Among the 1024 TFCI numbers, normally about 10 numbers or at most 100numbers are actually used in mobile communication system. Consequently,because the correlation values corresponding to all 1024 TFCI codingsequences are calculated in the aforementioned conventional decodingapparatus even though it is not important to calculate the correlationvalues corresponding to all 1024 TFCI coding sequences, there is aproblem that the processing amount and power consumption which arerequired to determine the TFCI number become large. Thus, when theaforementioned conventional decoding apparatus is built in acommunication terminal which is driven by a battery, there is a problemthat the using time of a communication terminal becomes short.

Moreover, when an error occurs with TFCI due to the influence of noiseand such in the propagation path, a case might result in the decodingapparatus where the correlation value calculated using a TFCI codingsequence having a close inter-code distance to a transmitted TFCI codingsequence becomes maximum. In the case when the TFCI number correspondingto TFCI coding sequence with a near inter-code distance is the TFCInumber which is not actually used, there is a problem that this TFCInumber which is not actually used is erroneously determined as thereceived TFCI number.

Because the data will be decoded by an erroneous transmission formatwhen the TFCI number is erroneously determined, all the data of TTI inrespect to which the transmission format is erroneously determined mightbe erroneously decoded, and hence, the error rate characteristics of thereceived data will be remarkably deteriorated.

SUMMARY OF INVENTION

It is an object of the present invention to provide a decoding apparatusand a decoding method that are capable to improve the TFCI determiningprecision while reducing the amount of processing and power consumptionwhich are required to determine the TFCI.

In order to achieve such an object, in the present invention, the TFCIis determined using only those actually used TFCI numbers as candidatesfrom among a plurality of TFCI numbers. Therefore, it is possible toimprove the TFCI determining precision while reducing the processingamount and power consumption that are required to determine the TFCI.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a decodingapparatus according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to Embodiment 2 of the present invention.

FIG. 3 is a flowchart showing an operation of a decoding apparatusaccording to Embodiment 2 of the present invention.

FIG. 4 is a block diagram showing a configuration of a decodingapparatus according to Embodiment 3 of the present invention.

FIG. 5 is a flowchart showing an operation of a decoding apparatusaccording to Embodiment 3 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be specifically describedhereinafter with reference to the accompanying drawings.

(Embodiment 1)

FIG. 1 is a block diagram showing a configuration of a decodingapparatus according to Embodiment 1 of the present invention. Thedecoding apparatus shown in FIG. 1 is built in, for instance, acommunication terminal apparatus such as, a cellular phone and such usedin a mobile communication system. For example, such a communicationterminal apparatus carries out radio communication based on CDMAtechnology. Moreover, in the following description it is assumed thatthe TFCI transmitted from a communication partner is shown by one TFCInumber from among the 1024 TFCI numbers from the 0 through 1023 using 10bits and transmitted after being converted into TFCI coding sequence of32 bits.

In the decoding apparatus shown in FIG. 1, demodulation section 101demodulates the received signal including TFCIs, and outputs the TFCIportion in the demodulated received signal to TFCI memory 102 whileoutputting the data portion to data memory 103. In addition, each bit ofTFCIs is distributed into a predetermined position of each slot of thereceived signal and it is difficult to carry out TFCI determinationuntil TFCIs of one frame are received in the decoding apparatus.Accordingly, TFCI memory 102 accumulates TFCIs of one frame. Moreover,data memory 103 accumulates data of one frame.

Since the group of TFCI numbers that may actually be used (hereinafter,the group of TFCI numbers that may actually be used is referred to as“the group of TFCI numbers in use”) for every communication channel isspecified by a layer which is upper than the physical layer(hereinafter, simply it is referred to as “upper layer”) in the mobilecommunication system, candidate limiting section 104 is notified fromupper layer with the group of TFCI numbers in use.

Candidate limiting section 104 has a table that shows the correspondencerelation between the TFCI number and TFCI coding sequence. Further,candidate limiting section 104 outputs to correlation value calculatingsection 105 only the TFCI coding sequences corresponding to TFCI numbersthat are actually used among the 1024 TFCI numbers from the 0 through1023 referring to the table based on each TFCI number that is includedin the group of TFCI numbers notified from upper layer. That is to say,candidate limiting section 104 limits the candidates for TFCI to anactually used N TFCIs among the 1024 TFCIs.

Correlation value calculating section 105, by way of calculating thecorrelation values between the coding sequences outputted from candidatelimiting section 104 and the received TFCI, calculates correlationvalues using only those actually used TFCI numbers as candidates fromamong the 1024 TFCI numbers from the 0 through 1023. That is,correlation value calculating section 105 calculates correlation valuesbetween each of TFCI coding sequences corresponding to the actually usedTFCI numbers and the received TFCI. Correlation value calculatingsection 105 outputs each of the calculated correlation values along withthe TFCI number to correlation value memory 106. Moreover, it ispossible to perform a high speed calculation of the correlation value byusing, for instance, a high speed Hadamard transform for correlationvalue calculation.

Correlation value memory 106 stores correlation values outputted fromcorrelation value calculating section 105 in correspondence with theTFCI numbers.

Maximum value detecting section 107 detects the maximum correlationvalue among correlation values stored in correlation value memory 106.Then, maximum value detecting section 107 notifies error correctiondecoding section 108 of the TFCI number corresponding to the maximumcorrelation value.

Error correction decoding section 108 specifies the transmission formatof the data accumulated in data memory 103 based on TFCI number notifiedfrom maximum value detecting section 107, and performs error correctiondecoding on the data accumulated in data memory 103 based on thespecified transmission format. In addition, the error correctiondecoding is performed based on, for instance, Viterbi algorithm.

Operation of the decoding apparatus which has the aforementionedconfiguration will be explained below.

Only the TFCI coding sequences corresponding to TFCI numbers included inthe group of TFCI numbers in use notified by the upper layer isoutputted to correlation value calculating section 105 from candidatelimiting section 104.

Correlation values between the TFCI coding sequences outputted fromcandidate limiting section 104 and TFCI of one frame accumulated in TFCImemory 102 are calculated in correlation value calculating section 105.In other words, only the correlation values corresponding to theactually used N TFCI numbers among the 1024 TFCI numbers are calculatedin correlation value calculating section 105.

For example, when the actually used TFCI numbers is limited to 30, eachcorrelation value between the TFCI coding sequence corresponding to eachnumber of those 30 and the TFCI of one frame accumulated in TFCI memory102 is calculated. According to this example, since 30 correlationvalues are calculated in comparison with the 1024 correlation valueshaving been conventionally calculated, it is possible to reduceremarkably the processing amount and power consumption required for thecorrelation value calculation processing which is one process ofdetermining processes of TFCIs.

The calculated N correlation values along with the corresponding TFCInumbers are outputted to correlation value memory 106. N correlationvalues and the corresponding TFCI numbers are stored in correlationvalue memory 106.

The maximum correlation value among the correlation values stored incorrelation value memory 106 is detected in maximum value detectingsection 107. Then, the TFCI number corresponding to the maximumcorrelation value is determined as a number of TFCI that is accumulatedin TFCI memory 102 (i.e., the received TFCI). The determined TFCI numberis notified to error correction decoding section 108.

As described above, when an error is occurred in the TFCI due to theinfluence of noise and such in the propagation path, there is a case inthe aforementioned conventional decoding apparatus that the correlationvalue corresponding to the TFCI number which is not actually usedbecomes the maximum, and the number of the received TFCI is erroneouslydetermined.

On the other hand, in the decoding apparatus according to the presentembodiment, the correlation values subject to determination in maximumvalue detecting section 107 are limited to the N correlation valuescorresponding to the actually used TFCI numbers. That is to say, it ispossible to prevent the correlation value corresponding to the TFCInumber which is not actually used to be detected as the maximum inmaximum value detecting section 107.

Thus, in the decoding apparatus according to the present embodiment, theprobability that TFCI is erroneously determined is minimized and thedetermination accuracy of TFCI is improved compared to theaforementioned conventional decoding apparatus. Hence, it is possible toprevent the deterioration of error rate characteristics of the receiveddata.

In error correction decoding section 108, the transmission format of thedata accumulated in data memory 103 is specified based on TFCI numbernotified from maximum value detecting section 107. Then, the dataaccumulated in data memory 103 is subjected to error correction decodingbased on the specified transmission format. Accordingly, a data of oneframe subjected to error correction decoding processing is obtained.

Therefore, according to the present embodiment, it is possible toimprove the TFCI determination precision while reducing the amount ofprocessing and power consumption required to determine the TFCI byperforming. TFCI determination by using only those actually used TFCInumbers as candidates from among a plurality of TFCI numbers.

(Embodiment 2)

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to Embodiment 2 of the present invention. As shownin this figure, in addition to the decoding apparatus shown in FIG. 1,the decoding apparatus according to the present embodiment is furtherprovided with threshold value deciding section 201, controlling section202, memory updating section 203 and CRC section 204. In FIG. 2,however, the corresponding similar sections shown in FIG. 1 are assignedthe same reference numerals and explanations thereof are omitted.

In the decoding apparatus shown in FIG. 2, threshold value decidingsection 201 decides whether the maximum correlation value detected bymaximum value detecting section 107 is above a predetermined threshold.Threshold value deciding section 201 notifies error correction decodingsection 108 of TFCI number corresponding to the correlation value whensuch a correlation value is above a predetermined threshold, and whenthe correlation value is below the predetermined threshold, it notifiescontrolling section 202 of such a result along with TFCI number.Controlling section 202 controls the operation of maximum valuedetecting section 107 and memory updating section 203 based on aninstruction from threshold value deciding section 201 and CRC section204.

Memory updating section 203 updates a correlation value that isdetermined to be below the predetermined threshold value in thresholdvalue determining section 201 and a correlation value that correspondsto a TFCI number that is used upon error correction decoding of the datawith which an error is detected in CRC section 204 into a value thatcannot be detected as a maximum value (for instance, 0 value) from thecorrelation values stored in correlation value memory 106 based on ainstruction from controlling section 202. In addition, the explanationof how the correlation value is updated as “0” by memory updatingsection 203 will be given below.

CRC section 204 uses an error detecting code such as CRC which isincluded in the data subjected to error correction decoding(hereinafter, simply referred to as “decoded data”) to perform an errordetection processing on the decoded data. Then, CRC section 204 outputsonly the decoded data of which an error is not detected along with CRCresult. Further, when an error is detected in the decoded data, CRCsection 204 notifies controlling section 202 of an error-detectedcommand along with the TFCI number while discarding the decoded data.

Operation of the decoding apparatus which has the aforementionedconfiguration will be explained below. FIG. 3 is a flowchart showing anoperation of a decoding apparatus according to Embodiment 2 of thepresent invention.

First, in step (hereinafter, it is referred to as “ST”) 301, similar tothe aforementioned Embodiment 1, a correlation value is calculated fromthe candidates of actually used TFCI numbers in correlation valuecalculating section 105, and the calculated correlation value along withthe TFCI number is outputted to correlation value memory 106.

Next, in ST302, the maximum correlation value among correlation valuesstored in correlation value memory 106 is detected by maximum valuedetecting section 107. Then, maximum value detecting section 107 outputsthe maximum correlation value along with its corresponding TFCI numberto threshold value deciding section 201.

Moreover, maximum value detecting section 107 outputs a signal thatindicates the execution of maximum value detection to controllingsection 202. Controlling section 202 is provided with a counter forcounting the number of times of maximum value detection, and controllingsection 202 increments the counter by 1 whenever the signal whichindicates the execution of maximum value detection is outputted frommaximum value detecting section 107. Further, it is assumed that theinitial value of the counter is Then, in ST303, threshold value decidingsection 201 decides whether the maximum value detected by maximum valuedetecting section 107 is above the predetermined threshold. When thatmaximum value is below the predetermined threshold, threshold decidingsection 201 notifies controlling section 202 of such a result along withthe TFCI number. Further, when the maximum value is below thepredetermined threshold in ST303 then proceed to ST304.

Next, in ST304, the controlling section 202 decides whether the numberof times of the maximum value detection has reached the number N of theactually used TFCI numbers (hereinafter, it is referred to as “number ofTFCI numbers in use”) with reference to the counter value. In the mobilecommunication system as described above, because the group of TFCInumbers in use is specified for every communication channel by an upperlayer, controlling section 202 is notified of the number N of TFCInumbers in use, from the upper layer.

When the number of times of the maximum value detection does not reachthe number N of TFCI numbers in use, in ST305, controlling section 202notifies memory updating section 203 of the TFCI number notified fromthreshold value deciding section 201 and, furthermore, instructs memoryupdating section 203 to update the correlation value corresponding tothe TFCI number notified from threshold value deciding section 201 to“0”.

Following the instruction, the correlation value that has been decidedto be below the predetermined threshold in threshold value decidingsection 201 among correlation values stored in correlation value memory106 is updated as “0” by memory updating section 203. After updatingprocessing, memory updating section 203 outputs a signal that indicatesthe completion of updating processing to controlling section 202. Basedon such a signal, controlling section 202 instructs maximum valuedetecting section 107 to re-execute maximum value detection processingin ST302. Since the maximum value last detected in ST302 is alreadyupdated as “0”, with the processing of ST 302 of this time, acorrelation value that is next large to the maximum value last detectedin ST 302 is detected as the maximum value. Moreover, when the number oftimes of maximum value detection reaches the number N of TFCI numbers inuse in ST304, controlling section 202 stops the maximum value detectionoperation until next decoding timing while resetting the counter to “1”.

On the other hand, when the maximum value of the correlation valuedetected by maximum value detecting section 107 is above thepredetermined threshold in ST303, the TFCI number corresponding to sucha correlation value is notified to error correction decoding section 108by threshold value deciding section 201.

Then, error correction decoding section 108 specifies the transmissionformat of the data accumulated in data memory 103 based on TFCI numbernotified from threshold value deciding section 201 in ST306. After this,the data accumulated in data memory 103 is subjected to error correctiondecoding based on the specified transmission format. The decoded data isoutputted to CRC section 204.

Next, CRC section 204 performs error detection on the decoded data inST307. When an error was not detected, CRC section 204 outputs thedecoded data along with the CRC result, thereby, the decoding processingis finished. In this case, CRC section 204, further, notifies thecontrolling section 202 of an error-undetected command. According tosuch a notification command, controlling section 202 stops the maximumvalue detection operation until the next decoding timing while resettingthe counter to “1”.

On the other hand, when an error was detected, CRC section 204 notifiescontrolling section 202 of an error-detected command along with TFCInumber while discarding the decoded data. In this case, progressing toST304.

In ST305 after the processing of ST304, controlling section 202 notifiesmemory updating section 203 of the TFCI number notified from CRC section204 and, furthermore, instructs memory updating section 203 to updatethe correlation value corresponding to the TFCI number notified from CRCsection 204 to “0”. Following the instruction, memory updating section203 updates the correlation value corresponding to the TFCI number usedat the time of error correction decoding of the data with an errordetected in CRC section 204 among correlation values stored incorrelation value memory 106 to “0”. After updating processing, memoryupdating section 203 outputs a signal that indicates the completion ofupdating processing to controlling section 202. Based on such a signal,controlling section 202 instructs maximum value detecting section 107 tore-execute maximum value detection processing in ST302.

Hereafter, the correlation values stored in correlation value memory 106are detected by maximum value detecting section in order from largerones, and until such detected correlation value becomes above apredetermined threshold and until no error is detected with the decodeddata decoded based on the TFCI number that corresponds to the detectedcorrelation value, above the aforementioned processing are repeatedmaximum of N times.

Therefore, according to the present embodiment, because only the TFCInumber corresponding to the correlation value that becomes above apredetermined threshold value is determined as the received TFCI number,it is possible to improve the determination reliability of the TFCI.

Moreover, because the TFCI determination and data decoding are carriedout repeatedly until an error is no longer detected in the decoded datathat is decoded based on the TFCI number corresponding to thecorrelation value which becomes above the predetermined threshold, it isalso possible to improve the decoding reliability of data.

(Embodiment 3)

FIG. 4 is a block diagram showing a configuration of a decodingapparatus according to Embodiment 3 of the present invention. As shownin this figure, the decoding apparatus according to the presentembodiment is provided with transmission power control informationgenerating section 401 in addition to the decoding apparatus shown inFIG. 2. Further, the corresponding similar sections shown in FIG. 2 areassigned the same reference numerals in FIG. 4 and explanations thereofare omitted.

In the decoding apparatus shown in FIG. 4, transmission power controlinformation generating section 401 generates transmission power controlinformation to instruct the communication partner to increase the signaltransmission power based on a instruction from controlling section 202.

Operation of the decoding apparatus which has the aforementionedconfiguration will be explained below. FIG. 5 is a flowchart showing anoperation of a decoding apparatus according to Embodiment 3 of thepresent invention. Moreover, the corresponding similar operational stepsshown in FIG. 3 are assigned the same reference numerals in FIG. 5 andexplanations thereof are omitted.

When in ST304 the counter provided in controlling section 202 reachesthe number N of TFCI numbers in use, in ST501, controlling section 202instructs transmission power control information generating section 401to generate transmission power control information to instruct thecommunication partner to increase signal transmission power.Transmission power control information generating section 401 generatestransmission power control information such as TPC (Transmission PowerControl) bit to instruct the communication partner to increase signaltransmission power based on a instruction from controlling section 202,and outputs this transmission power control information to thetransmission part inside a communication terminal apparatus. In thistransmission part, the transmission power control information is mappedinto a transmission signal and transmitted to the communication partner(base station). The communication partner increases the transmissionpower of the signal including the TFCI based on the receivedtransmission power control information.

That is, when the total of both, the number of correlation values whichare below the predetermined threshold value and the number of thedecoded data in which the error is detected, reaches the number N ofTFCI numbers in use, the decoding apparatus according to the presentembodiment decides that the channel environments are inferior, andinstructs the communication partner to increase the transmission powerof the signal including TFCI.

According to the present embodiment, because the transmission power ofthe signal including the TFCI is increased in the communication partnerside when the channel environments are inferior, it is possible toimprove the receiving quality of TFCI. Thus, since it is possible toreceive the TFCI with good receiving quality regardless to the channelenvironment, even when the channel environments are inferior, the TFCIcan be determined correctly and it is possible also to preventdeterioration of the decoding characteristics of data.

In addition, the decoding apparatus according to the aforementionedEmbodiments 1-3 can be built in a communication terminal apparatus orbase station apparatus that carries out communication with thiscommunication terminal apparatus employed in a radio communicationsystem. In such a case, because the error rate characteristics areimproved by improving the TFCI determination accuracy in bothcommunication terminal apparatus and base station apparatus, it ispossible to enhance and improve the data communication quality, speechquality, etc.

As described above and according to the present invention, while beingable to improve the determination accuracy of TFCI, the processingamount and power consumption required for TFCI determination can bereduced.

The present application is based on the Japanese Patent Application No.2000-362431 filed on Nov. 29, 2000, entire content of which is expresslyincorporated by reference herein.

1-9. (Canceled).
 10. A decoding method for a communication terminalapparatus in a mobile communication system, said method comprising: (a)receiving notification of transport format combination indicators(TFCIs); (b) limiting transport format combination indicator (TFCI)candidates, for received data, to said TFCIs, identified in accordancewith said notification; (c) determining a TFCI, from among the TFCIcandidates limited in step (b), for said received data; and (d)obtaining decoded data by decoding said received data in accordance withthe TFCI determined in step (c).
 11. A communication terminal apparatusin a mobile communication system, said apparatus comprising: a receiverthat receives notification of transport format combination indicators(TFCIs); a limiter that limits transport format combination indicator(TFCI) candidates, for received data, to said TFCIs identified inaccordance with said notification; a determiner that determines a TFCI,from among the TFCI candidates limited by said limiter, for saidreceived data; and a decoder that obtains decoded data by decoding saidreceived data in accordance with the TFCI determined by said determiner.